I have isolated cortical neurons from mouse pups ( day1) and seeded on poly d lysine coated wells of 24 well plated (120000cells/well) and cultured in a medium composed of Neurobasal A, Glutamax, pen/strep and B27. After 2 DIV the cells appears like neurospheres ans they started to show processes and get connected to each other. why neurosphere like structures appear in primary cortical neuronal culture?